关键词: 城市交通, 外部成本, 价值链, 城市轨道交通, 内部成本, 外部性

Abstract: Nowadays，urban rail transit has been the most effective solution to traffic congestion because of its fast，efficient，safe，energy saving and environmental protecting characteristics. However，the high cost of rail projects and the operation maintenance，together with the social problems brought by the urban rail transit such as noise pollution，traffic accidents and air pollution have become the “bottleneck” of its healthy development. This paper systematically analyzes the internal and the external costs of Beijing Subway Line 4 as an example. Based on the value chain theory，the internal cost is divided into preliminary planning and designing cost，constructing cost and operating cost. On the other hand，the external cost is classified into the cost of air pollution，traffic accident and noise pollution. The external cost is quantified，incorporated into the total cost of rail transportation as well. This research provides the basis for the government to formulate the fare by accurate calculation of the total cost of urban rail transit. Moreover，this research promotes the sustainable development of economic resources，social resources and environmental resources.

Key words: urban traffic, external cost, value chain, urban rail transit, internal cost, externality